High voltage-activated (HVA) calcium channels are essential for diverse biological processes ranging from gene regulation and cell growth to neurotransmitter release and muscle contraction. They are made up of several subunits, including alphal, alpha2-delta and beta. Although the beta subunit is only an auxiliary subunit, it is essential for trafficking the channel complex to the surface membrane and for the proper function of the channel. Other signaling proteins, such as G proteins and Rem/Rad/Gem(Kir) (RGK) family of small GTPases, regulate the activity of HVA calcium channels by either indirectly or directly interact with the beta subunit. Thus, the beta subunit is crucial for regulating the magnitude and kinetics of calcium signaling in excitable cells. Our group and two other groups have recently obtained high-resolution crystal structures of the beta subunit in complex with its primary binding partner in the alpha 1 subunit. This research proposal will combine x-ray crystallography, biochemistry and electrophysiology to further study the structure and function of the beta subunit and its interactions with other proteins, using the new structures as a blueprint. We will study: (1) the structural and biophysical mechanisms of regulation of HVA calcium channels by the beta subunit; (2) the interplay between regulation of HVA calcium channels by the beta subunit and G protein beta-gamma subunit; and (3) the structural and biophysical mechanisms of regulation of HVA calcium channels by the RGK GTPases. Mutations in the beta subunit cause human diseases such as idiopathic generalized epilepsy and episodic ataxia and a mutation in a RGK GTPase has been linked to congestive heart failure. These studies therefore may not only provide new insights into the basic mechanisms of calcium channel function and regulation but also new therapeutic strategies for treating neurological and cardiovascular diseases.